In the art of packaging meat, fish, poultry, vegetables, fruits, or other food products, it has been a problem to provide for relatively long shelf life of the packaged goods in a package that will not adversely affect the appearance or keeping qualities of the packaged goods, is relatively simple and inexpensive to manufacture, yet sufficiently robust to protect the packaged goods from damage and spoilage. It is also desirable to control the exposure of the contents to certain gases such as oxygen and carbon dioxide. Some products, such as fresh fish, must be packaged in a package with specific gas permeability properties to ensure food safety. For example, fresh fish is packaged in sufficient oxygen gas to prevent the growth of anaerobic bacteria.
Vacuum skin packaging is a common method of packaging many articles. Skin packaging is a known technique where goods are tightly packaged within a wrapping material and where substantially all of the atmospheric air is excluded. Often the goods are placed in a tray or on a board background to increase the rigidity of the package to allow for better merchandising. When used, the trays or boards are typically prepared with a moisture-impermeable surface to prevent their degradation by moisture from the packaged food product. However, the surface is impermeable not only to moisture, but oxygen as well. In the case of fresh fish, use of an impermeable backing, such as a typical board, base or tray, is not acceptable because the backing blocks the oxygen from contacting the fish.
Packaging has also been known to include certain gases to enhance the keeping qualities of the contents (modified atmosphere packaging). The shelf life of the packaged goods can thereby be enhanced. Typically these packages are made from a plastic material that provides a barrier to the egress of desired gases or the ingress of unwanted gases. In other cases, the plastic material may be such that it allows gases that may be generated within the package to escape. Other known plastic materials allow certain gases to permeate to enhance the keeping qualities of the packaged goods. Films with high oxygen permeability comprising blends of highly neutralized organic acid and ethylene acid copolymers have been disclosed in PCT patent application publication WO03/089240.
U.S. Pat. Nos. 4,685,274; 4,840,271; 5,025,611; 5,103,618 and 5,115,624 describe packages, methods, and apparatus for packaging perishable goods. The packages described therein comprise a semi-rigid or rigid base, typically a tray, perishable goods on the base, a flexible gas permeable plastic web over the goods and the base to at least partially skin pack the goods, and a lid for the base. A package according to these patents also comprises a gas impermeable outer package to provide a headspace that retains a gas selected for enhancing preservation of the packaged goods by permeation of the gas through the gas permeable web. However, these packages are able to retain only a limited volume of the gas in the headspace.
Therefore, it is desirable to provide a moisture-resistant, gas permeable semi-rigid or rigid structure suitable for use as a board, base or tray for packaging food products that require breathable (e.g. oxygen and/or carbon dioxide permeable) packages. The packages can include highly oxygen- and/or CO2-permeable compositions useful as coatings or laminates for rigid or semi-rigid structures for packaging.